Light control device

ABSTRACT

There is provided a light control device wherein a magnetic fluid consisting of a colloidal solution prepared by mixing together a powdered activated magnetic material such as nickel, cobalt, iron or various iron oxides and oleic acid, heptane or the like and a substance transparent to light such as glycerin or silicone oil are placed within a hermetically sealed container, whereby the position of the magnetic fluid is controlled by the imposition of an external magnetic field to transmit and intercept light.

DU-CO I United States Patent 1 Iwata Oct. 7, 1975 [54] LIGHT CONTROLDEVICE 3,322,482 5/1967 Harmon 350/267 1 1 Inventor: Hiroshi 1m, OsakaJapan 313312;? 211333 Z*Jf.f..f..j.jjjjijj.... [73] Assigneez w ElectricCompany, Ltd" 3,648,269 3/1972 Rosenweig et al 350/267 X Osaka, Japan[22] Filed: Aug 16, 1973 Primary Examiner-Vincent P. McGraw AssistantExaminer-Paul K. Godwin PP N05 388,763 Attorney, Agent, or Firm-Stevens,Davis, Miller &

Mosher [30] Foreign Application Priority Data Aug. 18, Japan Sept. 20,1972 Japan 47-94763 Sept. 20, 1972 Japan 47-94764 There is provided alight control device wherein a Sept. 20, 1972 Japan 47-94765 magneticfluid consisting of a colloidal solution pre- Oct. 12, 1972 Japan47-102529 pared by mixing together a powdered activated mag- 7 neticmaterial such as nickel, cobalt, iron or various 3 6 354/226 iron oxidesand oleic acid, heptane or the like and a [51] Int. Cl. .f. G02B 9/14substance transparent to light such as glycerin or sili- Field Of Search350/ 266, 267; cone oil are placed within a hermetically sealed con-354/50, 29, 60, 226, 227, 234; 49/2 tainer, whereby the position of themagnetic fluid is controlled by the imposition of an external magnetic[56] References Cited field to transmit and intercept light.

UNITED STATES PATENTS 3,215,572 11/1965 Papell 149/2 8 12 Draw"; F'guresamt U.S. Patent 0a. 7,1975 Sheet 1 of 4 3,910,687

* \Hm; I mm [411/ 2 US. Patent 0m. 7,1975 Sheet4 of4 3,910,687

CONSTANT fil CIRCUIT l5 i6 27 rvmsruenzxxnow (IJNVERSION CIRCUITTlME-(DNSTANT CIRCUIT LIGHT CONTROL DEVICE BACKGROUND OF THE INVENTIONFIELD OF THE INVENTION The present invention relates to a light controldevice employing a magnetic colloidal fluid and magnetic fieldgenerating means.

DESCRIPTION OF THE PRIOR ART Optical shutters which are not based on theuse of conventional mechanical means have been proposed, in which asubstance that utilizes the so-called polarization phenomenon of lightaccording to the Kerr effect or the Faraday effect, i.e., the doublerefraction phenomenon of light or the rotation of the vibration plane ofa linearly polarized light caused by the application of a strongelectric field or magnetic field to a dielectric material, andpolarizers for producing linearly polarized light are arranged in theform of sandwich and an external electric field or magnetic field isapplied to the dielectric substance to vary the rotary polarized lightand thereby to control the transmission of the light, or alternately anorganic substance, e.g., a so-called liquid crystal plate ofparticularly the nematic type is used so that the molecular orientationof the substance is disturbed by the imposition of an external electricfield to effect the double refraction of the light and thereby tocontrol the transmission of the light.

A disadvantage of the former which is based on the use of the dielectricsubstance and the rotary polarized light is that since the operatingprinciple of the device requires the polarizers for producing linearlypolarized light be placed respectively on the front and back sides ofthe device, the incident light is inevitably decreased considerably asit passes through the polarizers. Particularly, if the device isincorporated for example in photographic cameras which are subject toconstant efforts to use as bright a lens system as possible to ensure anincreased incident light, such a loss in the incident light is a seriousproblem. Further, the means for generating the required electric fieldor magnetic field generally tends to become bulky and elaborate andtherefore the device cannot lend itself for use in conjunction withapparatus intended to be carried on a person.

On the other hand, a disadvantage of optical control devices of thelatter type employing the liquid crystalline phenomenon of the nematictype is that since the liquid crystal is normally transparent to light,that is, it is rendered opaque by the imposition of an electric field,if it is used for example as a shutter for photographic cameras, theelectric field must be normally applied to the liquid crystal plate tomeet the requirement that the passage of light be normally intercepted,thus requiring considerable power consumption and making practical useof the device impossible.

In addition, the use of either one of these photoelectric phenomena hasa drawback in that since the resultant device is based on the use of thepolarization phenomenon of light, there is a relationship between theincident light and the transmitted light which depends on the wavelengthof light; that is, the operating principle is such that it is impossibleto completely intercept the light and at the same time to provide itwith a flat transmission characteristic which has no dependency on thewavelength for transmission.

SUMMARY OF THE INVENTION It is the object of the present invention toprovide an entirely novel light control device which overcomes theabove-mentioned deficiency and in which a magnetic colloidal fluid issuspended in a medium which is transparent to light, whereby theposition of the magnetic fluid is controlled in accordance with thestrength of a magnetic field.

In accordance with the present invention, there is thus provided a lightcontrol device which is not subject to any mechanical restrictions suchas those which are due to the shutter speed and which is capable ofperforming very high-speed opening and closing operations.

DESCRIPTION OF THE DRAWING FIg. l is a schematic diagram useful forexplanining the principle of the present invention.

FIG. 2 is a schematic view showing the construction of a light controldevice according to an embodiment of the present invention.

FIG. 3A is a partial side view of the device shown in FIG. 2.

FIG. 3B is a plan view of the device of FIG. 3A.

FIG. 4A is a partial side view of another embodiment of the deviceaccording to the present invention.

FIG. 4B is a plan view of the device of FIG. 4A.

FIG. 5 is a schematic view showing the construction of still anotherembodiment of the present invention.

FIG. 6 is a schematic view showing an exemplary distribution of themagnetic fluid used with the present invention.

FIG. 7A is a side view showing the construction of magnetic fieldgenerating means used in still another embodiment of the presentinvention. 5

FIG. 7B is a plan view of the device of FIG. 7A.

FIG. 8 is a schematic view showing the construction of still anotherembodiment of the present invention.

FIG. 9 is a schematic diagram showing the construction of still anotherembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description ofpreferred embodiments of the present invention, the general descriptionof magnetic fluid as for example disclosed in US. Pat. No. 3,215,572will be made hereunder.

An activated magnetic material such as nickel, cobalt, iron or any ofvarious iron oxides is milled in a stainless steel ball mill to producethe activated magnetic material having a partical size betweenapproximately 0.06 to 0.24 micron and the material is then mixed witholeic acid, heptane or the like to produce a colloidal solution in whichthe finely powdered magnetic material is properly distributed in thedispersion medium such as oleic acid. Thus, the resultant magnetic fluidis one in which the colloidal solution itself performs its function bythe imposition of an external magnetic field.

In a device wherein such a magnetic fluid is distributed, with a propervolume ratio, in a liquid base of a different kind such as water,glycerin or silicone oil transparent to light and contained in ahermetically sealedcontainer, the magnetic fluid and the liquid base arenot mixed together, but the magnetic fluid is suspended in the liquidbase and therefore the operation of the magnetic fluid such as themovement and fixing of the magnetic fluid in the hermetically sealedcontainer can be readily effected at all times in accordance with theapplication of an external magnetic field.

FIG. 1 shows a schematic diagram for use in explaining the baseprinciple of the light control device according to the presentinvention. A magnetic fluid 2 and a liquid base 3 of a materialtransparent to light are sealed in a hermetically sealed transparentcontainer 1 so that when a magnetic flux 4 is applied in the mannershown in FIG. I, the magnetic fluid 2 is gathered in the same shape asthe transmitted flux 4.

In this device, the material used to intercept the passage of lightcomprises an activated magnetic material such as nickel, cobalt or ironand therefore when the light is interrupted, the transmission of thelight is completely shut off and moreover the transmission of light inthe visible range has no dependency on the wavelength. Thus, if themagnetic flux 4 is controlled to move and fix the magnetic fluid 2 inthe transparent container 1, the function of a light control device suchas a shutter can be accomplished.

In FIG. 2 showing an exemplary embodiment of the above-described lightcontrol device according to the present invention, the present inventionis applied to a shutter for a camera unit, for example. A light controlelement 7 comprising the previously described magnetic fluid, etc. isdisposed in front of the film exposure section of an opticallyintercepted cartridge 5 for photographic film or the like. To normallyintercept the passage of an incident light 12 through a lens 13, apermanent magnet 8 made for example of barium ferrite has its magneticdomains magnetized as shown at 9 and in FIG. 2 and it is disposed at theback of a lightsensitive material 6 such as a photographic film so thatthe magnetic field produced by the magnetized domains 9 and 10 isapplied to the magnetic fluid of the light control element 7 and thusthe magnetic fluid is gathered by the magnetic flux to intercept thepassage of the light to the light-sensitive material 6 such as the film.

This is shown in greater detail in the plan view of FIG. 3B. As will beseen from FIG. 3B, the permanent magnet 8 is magnetized so that themagnetic domains 9 and 10 are magnetized horizontally and thus theresultant magnetic flux spread horizontally. Consethe electromagnet 14to permit the transmission of the light to the light-sensitive material6.

Accordingly, with the switch 15 arranged so that the supply of energyfrom the DC power supply 16 is enabled only for a period of timerequired to permit the passage of light to the light-sensitive material,e.g., the film 6, the transmission of light can be controlled by theopening and closing of the switch 15. Thus, by incorporating the lightcontrol device of this invention in a camera unit, the function of ashutter having no mechanical elements can be provided.

Against these advantages there is, however, a disadvantage due to theoperating principle of the invention itself. That is, since theinterception of the incident light is based on the use of theabove-described means for indirectly fixing the magnetic fluid by meansof the magnetic flux of the permanent magnet, etc., there is the dangerthat the application of astrong external mechanical shock or a strongexternal local magnetic field tends to momentarily expose the sensitivesurface of a film 6 or the like to light.

The foregoing difficulty is overcome by the embodiment of this inventionshown in FIG. 5. This embodiment differs from the embodiment of FIG. 2in that a simple light shielding plate 21 of the type having for examplea single vane is disposed in the path of the incident light. In thisway, while the magnetic fluid is normally fixed by means of thepermanent magnet, etc. to intercept the passage of the light, the lightshielding plate 21 prevents any optical exposure due to the impact of ashock on the magnetic fluid. When the shutter quently, the magneticfluid of the light control element 7 placed in the path of the magneticflux is fixed in the shape shown by the hatching. Therefore, by placingthe light-sensitive material 6, e.g., a film in such a manner that it iscompletely covered by the magnetic fluid, the passage of the incidentlight to the light-sensitive material 6 can be completely intercepted.

To move the magnetic fluid from its fixed position so that the lightfalls on the light-sensitive material or the film 6, as shown in FIGS.4A and 48, an electromagnet 14 is disposed around the permanent magnet 8and an electromagnetic coil 17 is energized from a DC power supply 16through a switch 15 to magnetize the electromagnet 14. As a result, eachof the ends 18 and 19 of the electromagnet 14 produces a magnetic fluxwith the polarity shown. Accordingly, if sufficient energy is suppliedfrom the power supply 16 so that the magnetic flux of the electromagnet14 cancels that of the permanent magnet 8, the magnetic flux of thelight control element 7 can be moved to the north and south poles ofbutton for example is depressed, the light shielding plate 21 is movedfirst to permit the passage of the incident light toward thelight-sensitive material 6 or the section of a film and thereafter themagnetic fluid fixed by the permanent magnet 8, etc. is moved by thesupply of current to the electromagnetic coil 17 to obtain a desiredexposure characteristic.

While, in the embodiments described above, the magnetic fluid is fixedby means of the permanent magnet with the result that when the presentinvention is applied to a camera unit or the like where the lightintercepting property is required in the normal condition of the unit,the supply of external energy is completely eliminated and hence thedeficiency of the prior art is entirely overcome, there is still anotherdisadvantage in that if a distance 22 between the magnetized portions,i.e., the magnetic poles of the permanent magnet becomes too wide, theflux density varies at the unmagnetized portions of the permanent magnetwith the result that the thickness of the magnetic fluid in its fixedposition varies and thus it becomes uneven as will be seen from FIG. 6,thereby failing to completely intercept the passage of light to thelight-sensitive material, e.g., the film 6.

FIG. 7 illustrates still another embodiment of the present inventionwhich incorporates a modification to overcome the foregoing difficulty.In other words, the magnetic poles of a plurality of permanent magnetsare arranged as shown in FIG. 7 to ensure a uniform thickness of themagnetic fluid in the fixed position.

A magnetic material 24 of for example barium ferrite is employed and aplurality of magnetic poles are induced on one side of the material inthe form of a mosaic as shown at 23 and 25 in FIG. 7. This produces themagnetic flux distributed as shown by 26 and hence a magnetic fieldwhich is irregular microscopically, but substantially flat is produced.

Consequently, the magnetic fluid 2 disposed in the magnetic flux path isdispersed evenly with a substantially unifonn thickness and thus theforegoing difficulty is completely eliminated.

FIG. 8 illustrates still another embodiment of the present invention inwhich the exposure time (e.g., the speed of the shutter.) of the lightcontrol device is associated with the time-constant circuit of aphotographic camera. In this embodiment, the value of the electricresistance of the magnetic fluid is approximately 10 lOlQcm andelectrodes 28 and 29 are embedded in a portion of the light controlelement 7, e.g., at one side thereof.

Assume now that a switch 16 is closed, a current flows through theelectromagnetic coil 17 causing the magnetic field of the permanentmagnet 8 to be cancelled. Thus upon actuation of the electromagneticcoil 17, the magnetic fluid 2 is moved to both sides in the lightcontrol element 7 as shown in FIG. 8, and at the same time the openingis formed in the light control element 7 which permits light to pass tothe light-sensing material, e.g., a film 6. Since the electrodes 28 and29 are located in one side of the light control element 7 and since theboth electrodes 28 and 29 are now submerged in the electricallyconductive magnetic fluid 2, the electrodes 28 and 29 are electricallyshortcircuited.

Accordingly, if a time-constant circuit shown at 27 in FIG. 8 comprisesa known type of time-constant circuit for photographic cameras whichcomprises a resistor and a capacitor and if the time-constant circuit 27is designed to begin its' operation from the time of shortcircuiting ofthe electrodes 28 and 29 and the electromagnetic coil I7 is deenergizedafter the expiration of a predetermined time determined by the values ofthe resistor and capacitor in the time-constant circuit 27, the lighttransmission time (shutter speed) of the light control device can bevaried at any time in accordance with the time constant of thetime-constant circuit 27. The switch 16 may be constructed to cooperatewith, e.g., a shutter button of a camera. More specifically, operationof the time-constant circuit 27 is initiated by the decrease in theelectrical resistance between the electrodes 28 and 29 which occurs whenthey become submerged in the low resistance electrically conductivemagnetic fluid 2. In a conventional time-constant circuit of the typeused in conjunction with the shutter timing mechanism of a camera, asshown for example in US. Pat. No. 3,326,103 granted Dec. 9, 1964, thereduction in resistance causes a capacitor to be charged through aresistor. When the voltage across the capacitor reaches a predeterminedvalue, a switch is opened causing the coil 17 to be de-energized and themagnetic fluid 2 is returned to its initial state thereby completing theexposure of the film 6 to light.

FIG. 9 illustrates still another embodiment of the present invention inwhich the exposure time of the light control element 7 is alsoassociated with the timeconstant circuit 27 of a photographic camera.Referring to FIG. 9, as compared with FIG. 8, a portion of the lightcontrol element 7 at one side thereof is provided with a pickup coil 30wound about that portion of the light control element 7. In thisembodiment, the

magnetic property of the magnetic fluid 2 is utilized instead ofelectrical conductivity thereof in contrast to the device of FIG. 8.When a switch 16 is closed, the

magnetic fluid 2 flows into the portion of the light control element 7around which portion the pickup coil 30 is wound in the same manner asdescribed in connection with FIG. 8.

A magnetization conversion circuit 31 is designed to detect the movementof the magnetic fluid 2 and actuate the time-constant circuit 27.Specifically, the magnetization conversion circuit 31 may comprise aresonance circuit including the pickup coil 30 and a capacitor, and aswitching element to actuate the timeconstant circuit 27. When themagnetic fluid 2 which has a relatively high permeability, flows intothe pickup coil 30, the inductance of the coil varies and the resonancecircuit of the magnetization conversion circuit 31 becomes resonant andproduces a pickup signal. Then, the switching element of themagnetization conversion circuit 31 in response to the pickup signalactuates the time-constant circuit 27. Circuits of this type arewell-known, an example being shown in publication Electronics, Vol. 35,No. 23, page 1 I3 (1965). The operation and function of thetime-constant circuit 27 are the same as in the device of FIG. 8. Inthese embodiments illustrated in FIGS. 8 and 9, the movement of themagnetic fluid 2 not only controls directly the passage of light throughthe light control element 7, but also functions as a switching meanswhen associated with the suitable pickup coil 30 or electrodes 28 and29. The switching means in turn actuates another circuit such astime-constant circuit 27.

In an ordinary photographic camera employing a lens shutter, in thenormal conditions the interception of incident light is effected by theclosing of a mechanical shutter disposed at the front or back of thelens to prevent the passage of incident light to a light-sensitivematerial such as a film. a

On the other hand, in a photographic camera employing a focal planeshutter, the incident light transmitted through the lens is interceptedby means of rubberized curtains, metal plates or metal foils placed infront of a light-sensitive material such as a film.

Consequently, when these shutters are closed, their relatively rigidmechanical structures ensure a positive interception of the incidentlight in the normal conditions of the camera.

Considering the time of the opening operation in either of these typesof shutter, however, the lens shutter mainly employs a mechanicalstructure so that a plurality of the metal plates are gradually openedwith time, while the focal plane shutter has a mechanical structurecomprising front and rear curtains so that the gap between the curtainsis adjusted.

With these constructions, all of the known shutters are based on the useof mechanical elements and therefore their shutter speed is inevitablylimited by the spring pressure, mechanical friction and resistance, etc.With the presently available techniques, the shutter speed is limited to1/1000 1/2000 of a second.

On the contrary, the basic operating principle of the present inventionis based on the use of a magnetic fluid suspended in a medium andtherefore the device of this invention is practically unrestricted bypurely mechanical factors. Moreover, while the viscosities of theliquids have mutual influence on them, the magnetic fluid preparedaccording to the previously described method is particularly of lowviscosity and therefore in contrast to the mechanical shutters, thedevice of this invention is practically unrestricted with respect to theshutter speed and moreover very highspeed opening and closing operationsare possible by increasing the starting current of the electromagnet foractuating the magnetic fluid.

I claim:

1. A light exposure control device comprising:

a hermetically sealed container having a front surface and a backsurface with respect to the passage of incident light and containing animmiscible fluid transparent to light and a non light transmittingmagnetic colloidal fluid including an activiated magnetic material, v

means for locating, a light-sensitive member adjacent the back surfaceof said container, and

means for generating a magnetic field in close proximity to saidcontainer to shift the position of said magnetic fluid out of the lightpassage in said container, said light-sensitive member being exposed tolight through said immiscible fluid or shielded therefrom by saidcolloidal fluid in accordance with whether said magnetic field is beinggenerated.

2. A light exposure control device according to claim 1, wherein saidmagnetic field generating means comprises a permanent magnet.

33. A light exposure control device according to claim 1, wherein saidmagnetic field generating means comprises an electromagnetic coil.

4. A light control device according to claim 1, wherein said magneticfield generating means comprises a plurality of small magnets set inarray in the vicinity of said hermetically sealed container.

5. A light exposure control device according to claim 1, furtherincluding a time-constant circuit for controlling the time of energysupply to said electromagnetic coil.

6. A light exposure control device according to claim 5, furtherincluding a plurality of electrodes disposed in said hermetically sealedcontainer for actuating said time-constant circuit.

7, A light exposure control device according to claim 5, furtherincluding magnetic detecting means for detecting a magnetic variationcaused by the movement of said magnetic fluid in said hermeticallysealed container.

8. A light exposure control device according to claim 1 furthercomprising a light shielding plate disposed on the front surface side ofsaid container and in the vicinity thereof for intercepting said light,said light shielding plate being operable. to allow light to reach thefront surface of said container, immediately before the actuation ofsaid magnetic field generating means and shield the front surface ofsaid container after termination of generation of said magnetic field.

1. A light exposure control device comprising: a hermetically sealedcontainer having a front surface and a back surface with respect to thepassage of incident light and containing an immiscible fluid transparentto light and a non light transmitting magnetic colloidal fluid includingan activiated magnetic material, means for locating, a light-sensitivemember adjacent the back surface of said container, and means forgenerating a magnetic field in close proximity to said container toshift the position of said magnetic fluid out of the light passage insaid container, said light-sensitive member being exposed to lightthrough said immiscible fluid or shielded therefrom by said colloidalfluid in accordance with whether said magnetic field is being generated.2. A light exposure control device according to claim 1, wherein saidmagnetic field generating means comprises a permanent magnet.
 3. A lightexposure control device according to claim 1, wherein said magneticfield generating means comprises an electromagnetic coil.
 4. A lightcontrol device according to claim 1, wherein said magnetic fieldgenerating means comprises a plurality of small magnets set in array inthe vicinity of said hermetically sealed container.
 5. A light exposurecontrol device according to claim 1, further including a time-constantcircuit for controlling the time of energy supply to saidelectromagnetic coil.
 6. A light exposure control device according toclaim 5, further including a plurality of electrodes disposed in saidhermetically sealed container for actuating said time-constant circuit.7. A light exposure control device according to claim 5, furtherincluding magnetic detecting means for detecting a magnetic variationcaused by the movement of said magnetic fluid in said hermeticallysealed container.
 8. A light exposure control device according to claim1 further comprising a light shielding plate disposed on the frontsurface side of said container and in the vicinity thereof forintercepting said light, said light shielding plAte being operable. toallow light to reach the front surface of said container, immediatelybefore the actuation of said magnetic field generating means and shieldthe front surface of said container after termination of generation ofsaid magnetic field.